The present invention relates generally to a haptic interface system for providing force feedback sensations, and more particularly, to a haptic interface system employing a magnetically-controllable medium to provide resistance forces.
Haptic interface systems, also known as force feedback systems, provide an operator holding an interface device, such as a joystick, with xe2x80x9cfeelxe2x80x9d sensations corresponding to whatever is being controlled by the interface device. A common example of such a system is in computer games. In such games, the action on a video display and the movement of a joystick or steering device are coordinated with physical force imparted to the operator""s hand through the joystick or steering device, to provide a simulated xe2x80x9cfeelxe2x80x9d for events happening on the display. For example, in an auto racing game, when an operator steers a car around a sharp turn at high speed, the haptic interface system imparts force on the steering wheel to make it more difficult to turn the wheel into the curve. This force feedback simulates the centrifugal force of the car making the turn and the friction forces applied to the tires as they are turned. Thus, haptic interface systems provide remote simulation of the actual physical feeling associated with an action or event through force feedback.
Typical haptic interface systems include one or more motors connected to the interface device in order to impart the force feedback sensation. Typical motors include direct current (DC) stepper motors and servo-motors. If the interface device is a joystick, motors are used to impart force in an x-direction, in a y-direction, or in combination to provide force in any direction that the joystick may be moved. Similarly, if the interface device is a steering wheel, motors are used to impart rotational force in a clockwise or counterclockwise direction. Thus, motors are used to impart forces in any direction that the interface device may be moved.
In a system using a single motor, the motor may be connected to the interface device through a gear train, or other similar energy transfer device, in order to provide force in more than one direction. In order to enable one motor to be used in a system, a reversible motor is typically utilized to provide force in two different directions. Additionally, mechanisms are required to engage and disengage the various gears or energy transfer devices to provide force in the proper direction at the proper time. In contrast, other typical systems use more than one motor to provide force in the required directions. Thus, current systems utilize a number of differing approaches to handle the delivery of force feedback sensations.
Current haptic interface systems may be disadvantageous, however, for a number of reasons. One primary area of concern is the cost of such systems. One item greatly contributing to the cost of a typical system is the use of DC stepper and servo-motors, and reversible motors. These types of motors are very sophisticated, requiring the ability to change speeds or rotations per minute (rpm), maintain different speeds, and reverse rotational direction. These features require greater mechanical and electrical complexity, which equates to a comparatively very high cost. Further, these motors need to be small in size in order to keep the haptic interface system from becoming unwieldy. This additionally complicates their design and increases cost. Also, because of their relatively small size, the sophisticated motors typically required in a haptic interface system are only able to generate a limited amount of torque. As such, the operator of an interface device may easily be able to overcome the torque or force feedback supplied by the motor. Thus, providing a small, sophisticated motor for a haptic interface system is relatively very costly, and may result in insufficient force feedback.
Also disadvantageously, typical DC motors used in haptic interface systems are not designed to perform in the manner required by the system. In order to provide force feedback, typical systems use direct drive motors configured to mechanically engage the output shaft of the motor with the interface device. For example, the output shaft of a DC motor may be geared to a steering wheel shaft or linked to a slide or other mechanism controlling the movement of a joystick. When the motor engages the gear or slide, the motor drives the interface device to provide force feedback. The operator holding the interface device, however, typically opposes the force feedback. The opposing force supplied by the operator then works against the direction of the motor output, which tends to stall the motor. Not only does this opposing force tend to wear out and/or strip components within the motor, but the stall condition leads to the generation of higher electric currents within the motor, straining the electrical components in the motor. Due to the repetitious nature of a haptic interface system, the reliability and longevity of motors in such haptic interface systems are severely reduced. Thus, motors used in typical haptic interface systems are typically not very well suited for the demanding environment in which they are operated.
Yet another disadvantage of current commercial haptic interface systems is that high impact forces from a motor connected to an interface device may be dangerous for the operator of the interface device. When the haptic interface system requires a quick, high impact force, a motor connected to an interface device may respond with a large force that may injure the operator if the operator is not ready for the abrupt force. This may be accounted for by ramping up the speed of the motor to achieve the force, but then the sensation becomes less realistic. Further, varying the engagement speeds of the motor complicates the software program that is used to run the haptic interface system, thereby further increasing cost. Thus, producing a realistic-feeling high impact force with current haptic interface systems may be dangerous to the operator or may require costly and complex system programming.
Some prior art devices have attempted to overcome some of the drawbacks of current haptic interface systems, with limited results. An electrorheological (ER) actuator, utilized in a force display system, is proposed by J. Furusho and M. Sakaguchi entitled xe2x80x9cNew Actuators Using ER Fluid And Their Applications To Force Display Devices In Virtual Reality Systems,xe2x80x9d in abstracts of the International Conference On ER Fluids, MR Suspensions and their Applications, Jul. 22-25, 1997 Yonezawa, Japan, pg. 51-52. An ER actuator comprises a device that contains an ER fluid, which is a substance that changes its shear strength with application of an electric field. The ER fluid can then be used as a clutch or a brake to increase resistance between two members.
The use of such an ER actuator is severely disadvantageous, however, for use in typical haptic interface systems, such as for computer games. One major issue is that an ER actuator presents a major safety problem because of the high electric voltage required to produce the electric field necessary to generate a desired change in shear strength in the ER fluid. For a haptic interface system, a typical ER fluid actuator may require voltages in the range of about 1000 to 5000 volts. Conversely, the motors used in the typical systems described above require in the range of about 500 milliamps (mA) to 1.0 A of current. Thus, the voltage required to operate an ER actuator is very high, making an ER actuator undesirable, and possibly unsafe, for a consumer device subject to a great amount of wear and tear.
Additionally, an ER actuator detrimentally requires expensive seals to hold the ER fluid within cavities within the actuator. Seals frequently wear, causing reliability problems for ER actuators and concerns about ER fluid leaks. Further, the use of seals typically requires machined parts having tight tolerances, additionally increasing the cost of the ER actuator. Also, ER actuators require expensive bearings to insure the relative positioning of the tight-tolerance parts.
Similarly, precise machining is required for the internal rotating components of an ER actuator, further increasing the cost of the actuator. Because an ER device requires a relatively large amount of surface area between the ER fluid and the two members that the ER fluid contacts, tight tolerance machining is needed between the multiple, adjacent surfaces of the members. Thus, a relatively large amount of surface area may be required to generate sufficient torque to provide the levels of force feedback required by typical haptic interface systems.
Finally, typical ER actuators that provide appropriate force may be too large to be integrated into a commercial haptic interface system. The device utilized to provide force feedback in a typical haptic interface system must be small and lightweight in order to be practically integrated into the system. An ER actuator meeting these requirements is very costly to produce, besides having the above-stated deficiencies. Thus, utilization of an ER actuator in a typical haptic interface system is not desirable.
Therefore, it is desirable to provide a haptic interface system that is more simple, cost-effective, reliable and better performing than the above-stated prior art.
According to a preferred embodiment of the present invention, a haptic interface system comprises a magnetically-controllable device that advantageously provides a variable resistance force that opposes movement of a haptic interface device to provide force feedback sensations. The haptic interface device is in operative contact with the operator who controls and responds to the interactive program. The magnetically-controllable device beneficially comprises a magnetically-controllable medium between a first and second member, where the second member is in communication with the haptic interface device. The magnetically-controllable medium provides the variable resistance force, in proportion to the strength of an applied magnetic field, that opposes relative movement between the first and second members. The system further comprises a computer system adapted to run an interactive program, a video display for displaying images associated with the interactive program and a sensor that detects the position of the haptic interface device and provides a corresponding variable input signal to the computer system.
The computer system processes the interactive program, and the variable input signal from the sensor, and provides a variable output signal corresponding to a semi-active, variable resistance force that provides the operator with realistic sensations corresponding to the interactive program. The variable output signal energizes a magnetic field generating device, disposed adjacent to the first and second members, to produce a magnetic field having a strength proportional to the variable resistance force. The magnetic field is applied across the magnetically-controllable medium, which is disposed in a working space between the first and second members. The applied magnetic field changes the resistance force of the magnetically-controllable medium associated with relative movement, such as linear, rotational or curvilinear motion, between the first and second members in communication with the haptic interface device. As such, the variable output signal from the computer system controls the strength of the applied magnetic field, and hence the variable resistance force of the magnetically-controllable medium. The resistance force provided by energizing the magnetically-controllable medium controls the ease of movement of the haptic interface device among a plurality of positions. Thus, the present haptic interface system provides an operator of an interactive program with realistic force feedback sensations through the magnetically-controllable device that opposes the movement of the haptic interface device.
In a preferred embodiment, the magnetically-controllable medium within the magnetically-controllable device is contained by an absorbent element disposed between the first and second member. The absorbent element may be compressed from a resting state, preferably in the amount of about 30%-70% of the resting state. The absorbent element may be formed as a matrix structure having open spaces for retaining the magnetically-controllable medium. Suitable materials for the absorbent element comprise open-celled foam, such as from a polyurethane material, among others.
The magnetically-controllable medium is a medium having a shear strength that varies in response to the strength of an applied magnetic field. One preferred type of magnetically-controllable medium is a magnetorheological fluid. As mentioned above, the magnetic-field generating device provides the applied magnetic field. The magnetic-field generating device is preferably a coil and comprises a wire having a number of turns and a certain gauge. The number of turns and gauge of the wire are dependent upon the desired range of the variable strength magnetic field and upon the electric current and voltage of the variable output signal.
The haptic interface device of the present invention may be any device in operative contact with the operator for controlling and responding to the interactive program, such as a video game. For example, a suitable haptic interface device may comprise a steering device and a joystick.
The computer system may comprise a host computer, a controller and an amplifier. The controller and amplifier, as is explained below, may alternatively be separate components or part of a haptic interface unit. The host computer comprises a processor that runs the interactive program. The controller comprises a microprocessor and firmware that are used to modify the variable input signal received from the sensor and the variable output signal received from the host computer. The controller then provides a modified variable input signal to the host computer and a modified variable output signal to the magnetically-controllable device. The modification function performed by the controller enables communication between the host computer and the magnetically-controllable device and the sensor. The amplifier further modifies the output signal to provide an amplified variable output signal in situations where the output signal from host computer is not sufficient to control the magnetically-controllable device. Further, the controller and amplifier may act as local processors, reducing the burden on the host computer by providing output signals for certain input signals, such as to provide reflex-like resistance forces, that do not need to be processed by the host computer.
In one embodiment, the present invention discloses a haptic interface unit comprising the magnetically-controllable device, as described above, adapted to provide a variable resistance force in proportion to a received variable output signal generated by a computer system processing an interactive program. The magnetically-controllable device further comprises a magnetic-field generating device, first and second members, and a magnetically-controllable medium. The magnetic-field generating device is energizable by the variable output signal to provide a variable strength magnetic field. The first and second members are adjacent to the magnetic field generating device. The magnetically-controllable medium is disposed between the first and second members, where the magnetically-controllable medium provides the variable resistance force in response to the variable strength magnetic field. Additionally, the haptic interface unit may further comprise a haptic interface device, adapted to be in operable contact with the operator, for controlling and responding to the interactive program. The haptic interface device is in communication with the magnetically-controllable device and has a plurality of positions, wherein an ease of movement of the haptic interface device among the plurality of positions is controlled by the variable resistance force. Finally, the haptic interface unit may further comprise a control unit that provides a signal to the magnetically-controllable device to control the variable resistance force.